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Abstract:

A pressure transmitter includes a sensor assembly having a hollow body
housing a pressure sensor. The pressure transmitter also includes a
support body which is made of a first material, and an interface body
which is connected to the support body and which is made of a second
material different from the first material. A first isolation diaphragm
is fixed onto the interface body and is made of the same material of the
interface body. The first isolation diaphragm is in fluid communication
with the pressure sensor and is configured for interfacing with a process
fluid.

Claims:

1. A pressure transmitter comprising: a sensor assembly having a hollow
body housing a pressure sensor; a support body which is made of a first
material; an interface body which is connected to the support body and is
made of a second material different from the first material; and a first
isolation diaphragm which is fixed onto the interface body, the first
isolation diaphragm being in fluid communication with the pressure sensor
and configured for interfacing with a process fluid, wherein the first
isolation diaphragm is made of the second material.

2. The pressure transmitter according to claim 1, wherein the interface
body is connected to the support body on a surface transverse with
respect to the first isolation diaphragm.

3. The pressure transmitter according to claim 1, wherein the interface
body is connected to the support body on a surface substantially parallel
to the first isolation diaphragm.

4. The pressure transmitter according to claim 1, wherein the interface
body is welded onto the support body along at least a first welding seam
provided on a surface which is spaced apart from the first isolation
diaphragm.

5. The pressure transmitter according to claim 1, comprising: a second
isolation diaphragm which is placed on the support body and in fluid
communication with the pressure sensor, wherein the first isolation
diaphragm is arranged so as to have substantially the same linear
displacement of the second isolation diaphragm when the first and second
isolation diaphragms are subject to substantially the same level of
pressure.

6. The pressure transmitter according to claim 5, wherein the second
isolation diaphragm is welded onto said support body.

7. The pressure transmitter according to claim 1, comprising: a second
isolation diaphragm which is fixed onto the interface body, the second
isolation diaphragm being in fluid communication with the pressure sensor
and configured for interfacing with a process fluid, wherein said second
isolation diaphragm is made of the second material.

8. The pressure transmitter according to claim 1, wherein said interface
body has a corrugated surface on which at least said first isolation
diaphragm is welded.

9. The pressure transmitter according to claim 1, wherein: the interface
body has a disc-shaped body embracing the support body and includes a
first portion and a second portion; and the first portion has a thickness
smaller than a thickness of the second portion.

10. The pressure transmitter according to claim 9, wherein the interface
body is welded onto the support body along a second welding seam located
at the first portion and spaced apart form the first welding seam.

11. The pressure transmitter according to claim 1, wherein the interface
body and the first isolation diaphragm are made of the second material
which is selected from the group consisting of: nickel-based alloys,
duplex and super-duplex stainless steels.

12. The pressure transmitter according to claim 2, wherein the interface
body is welded onto the support body along at least a first welding seam
provided on the surface which is spaced apart from the first isolation
diaphragm.

13. The pressure transmitter according to claim 12, comprising: a second
isolation diaphragm which is placed on the support body and in fluid
communication with the pressure sensor, wherein the first isolation
diaphragm is arranged so as to have substantially the same linear
displacement of the second isolation diaphragm when the first and second
isolation diaphragms are subject to substantially the same level of
pressure.

14. The pressure transmitter according to claim 13, wherein the second
isolation diaphragm is welded onto said support body.

15. The pressure transmitter according to claim 12, comprising: a second
isolation diaphragm which is fixed onto the interface body, the second
isolation diaphragm being in fluid communication with the pressure sensor
and configured for interfacing with a process fluid, wherein said second
isolation diaphragm is made of the second material.

16. The pressure transmitter according to claim 15, wherein: the
interface body has a disc-shaped body embracing the support body and
includes a first portion and a second portion; and the first portion has
a thickness smaller than a thickness of the second portion.

17. The pressure transmitter according to claim 16, wherein the interface
body is welded onto the support body along a second welding seam located
at the first portion and spaced apart form the first welding seam.

18. The pressure transmitter according to claim 3, wherein the interface
body is welded onto the support body along at least a first welding seam
provided on the surface which is spaced apart from the first isolation
diaphragm.

19. The pressure transmitter according to claim 18, comprising: a second
isolation diaphragm which is placed on the support body and in fluid
communication with the pressure sensor, wherein the first isolation
diaphragm is arranged so as to have substantially the same linear
displacement of the second isolation diaphragm when the first and second
isolation diaphragms are subject to substantially the same level of
pressure.

20. The pressure transmitter according to claim 19, wherein the second
isolation diaphragm is welded onto said support body.

21. The pressure transmitter according to claim 18, comprising: a second
isolation diaphragm which is fixed onto the interface body, the second
isolation diaphragm being in fluid communication with the pressure sensor
and configured for interfacing with a process fluid, wherein said second
isolation diaphragm is made of the second material.

22. The pressure transmitter according to claim 17, wherein the interface
body and the first isolation diaphragm are made of the second material
which is selected from the group consisting of: nickel-based alloys,
duplex and super-duplex stainless steels.

23. The pressure transmitter according to claim 21, wherein the interface
body and the first isolation diaphragm are made of the second material
which is selected from the group consisting of: nickel-based alloys,
duplex and super-duplex stainless steels.

Description:

RELATED APPLICATION

[0001] This application claims priority as a continuation application
under 35 U.S.C. §120 to PCT/EP 2009/058292 filed as an International
Application on Jul. 1, 2009 designating the U.S., the entire content of
which is hereby incorporated by reference in its entirety

FIELD

[0002] The present disclosure relates to a pressure transmitter. More
particularly, the present disclosure relates to a pressure transmitter
used to monitor physical variables in industrial processes, such as for
sensing the pressure of a fluid process, for example.

BACKGROUND INFORMATION

[0003] Pressure transmitters are devices which are utilized in industrial
process control systems in order to detect and/or measure the pressure of
a monitored process fluid. Such pressure transmitters can perform
differential or absolute pressure measurements and therefore are
manufactured according to different layouts and models. Most common
pressure transmitters are those indicated as gauge or absolute pressure
transmitters and differential pressure transmitters.

[0004] In many applications, the use of pressure transmitters is
particularly advantageous since from one or more measurements of
relative, differential or absolute pressure, it is possible to indirectly
obtain values that are indicative of other physical variables of the
fluid controlled, where such values would be more difficult to be
detected directly.

[0005] According to a known configuration, a pressure transmitter of
includes a main hollow body, sometime referred to as a module housing or
sensor housing body, which is suitably shaped to house components
carrying out the transduction. This main body includes a measurement
chamber housing a pressure sensor. Suitable primary electric/electronic
circuits for processing signals arriving from the pressure sensor may
also be housed into the main hollow body.

[0006] A transmitter body is coupled to the sensor housing body and
contains further components, such as, for example, displays for locally
displaying the values measured, secondary electronic circuits for
processing the signals arriving from the pressure sensor and for
communicating with other transmitters or with remote control units, etc.

[0007] In order to perform the required sensing and measurement
operations, the pressure transmitter includes a further part or body
which must be placed in contact with the process fluid. For this purpose,
the additional part is provided with one of more isolation diaphragms
which are in fluid communication with the pressure sensor and are
suitable to separate the process fluid from the circuit inside the
transmitter. At least one of the isolation diaphragms is positioned on
this additional part so as to have an external surface exposed directly
to the process fluid under monitoring.

[0008] This additional part can be a separate body connected to the sensor
housing body, for example, by screwing or welding, or it can be realized
monolithically with the sensor housing body.

[0009] At the current state of the art, although known pressure
transmitters can adequately perform the tasks they are required to
execute, there is still room for further improvements of their structure
and functioning.

[0010] For example, some possible drawbacks of known pressure transmitters
may result from the way the isolation diaphragms, and more specifically
the isolation diaphragms which directly interface with the process fluid
under control, are positioned on the body supporting them, especially
when pressure transmitters are used in very aggressive environments.

[0011] For instance, an isolation diaphragm is usually constituted by a
thin metallic membrane which is suitably welded onto its supporting body.
When the pressure transmitter is intended for being used in special
applications (e.g., environments with hot temperatures, and/or abrasive
or corrosive process fluids and so on), the isolation diaphragm is made
of special materials, such as nickel alloys.

[0012] When this thin membrane made of special material is welded on the
supporting body which is usually made of a common metallic material such
as a stainless steel, the thin membrane may partially melt and mix with
the stainless steel of the supporting body.

[0013] Hence, such a welding process, in addition to being quite
difficult, can result in a welding seam which is to some extent
defective. Furthermore, the mechanical characteristics of the isolation
diaphragm are deteriorated, and the isolation diaphragm itself may have
one or more points of inception of corrosion, which in some cases results
in the diaphragm having to be discarded.

SUMMARY

[0014] An exemplary embodiment of the present disclosure provides a
pressure transmitter which includes a sensor assembly having a hollow
body housing a pressure sensor. The exemplary pressure transmitter also
includes a support body which is made of a first material, and an
interface body which is connected to the support body and which is made
of a second material different from the first material. The exemplary
pressure transmitter also includes a first isolation diaphragm which is
fixed onto the interface body. The first isolation diaphragm is in fluid
communication with the pressure sensor and is configured for interfacing
with a process fluid. The first isolation diaphragm is made of the second
material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Additional refinements, advantages and features of the present
disclosure are described in more detail below with reference to exemplary
embodiments illustrated in the drawings, in which:

[0016] FIG. 1 is a schematic cross-section view illustrating an exemplary
embodiment of a pressure transmitter according to the present disclosure;

[0017] FIG. 2 is a schematic view illustrating, partially in
cross-section, an exemplary embodiment of a pressure transmitter
according to the present disclosure; and

[0018] FIG. 3 is an enlarged view of section "A" of FIG. 2.

[0019] In the following description and the appended drawings, components
equal or functionally equivalent to each other in the exemplary
embodiments described below will be indicated by the same reference
number for the sake of simplicity.

DETAILED DESCRIPTION

[0020] Exemplary embodiments of the present disclosure provide a pressure
transmitter which addresses and overcomes the drawbacks associated with
known configurations, as discussed above. For example, an exemplary
embodiment of the present disclosure provides a pressure transmitter
which includes a sensor assembly having a hollow body housing a pressure
sensor, and a support body which is made of a first material.

[0021] In accordance with an exemplary embodiment, the pressure
transmitter of the present disclosure can also include an interface body
which is connected to the support body and is made of a second material
different from the first material. The exemplary pressure transmitter of
the present disclosure can also include a first isolation diaphragm which
is fixed onto the interface body. The first isolation diaphragm is in
fluid communication with the pressure sensor and is configured for
interfacing with a process fluid. In accordance with an exemplary
embodiment, the first isolation diaphragm is made of the second material.

[0022] The pressure transmitter according to the present disclosure is
indicated as a whole with the reference numeral 1 in FIGS. 1 and 2. In
the example of FIG. 1, the pressure transmitter is illustrated as a gauge
pressure transmitter according to an exemplary embodiment, while in the
example of FIG. 2, the pressure transmitter is illustrated as a
differential pressure transmitter according to an exemplary embodiment.

[0023] As shown, the pressure transmitter 1 includes a sensor assembly
having a hollow main body 2 for housing a sensor, such as a pressure
sensor 3 whose structure and functioning, including circuitry, are known
to those skilled in the art and therefore will not be described herein in
further details. The hollow main body 2 is made of any suitable material,
for example, metallic material such as stainless steel.

[0024] As schematically illustrated in FIGS. 1 and 2, the pressure
transmitter 1 includes a transmitter body 30 which is suitably connected
to the sensor assembly, such as to the hollow body 2. The transmitter
body 30 houses electric/electronic circuitry 31 which receives input
signals from the pressure sensor 3, via connection elements 32 (e.g.,
cables). In accordance with an exemplary embodiment, the circuitry 31,
which can include a microprocessor, for example, elaborates input signals
received so as to output a measure of the pressure of a process fluid
which is monitored by the pressure transmitter 1 itself. For example, the
transmitter body 30 can be made of plastic and/or metallic material.

[0025] In the exemplary embodiments illustrated in FIGS. 1 and 2, the
pressure transmitter 1 also includes a support body 4 which is made of a
metallic material (hereinafter referred to as a "first material"), for
example, a common stainless steel such as AISI 316 L. As schematically
shown in the exemplary embodiments of FIGS. 1 and 2, the support body 4
is connected to the hollow body 2, for example, by means of soldering
and/or through screws. Alternatively, it would be possible to realize the
hollow body 2 and the support body 4 as a unique structurally monolithic
piece.

[0026] Further, the transmitter body 30 may also be realized in a single
piece with the hollow body 2 and shaped so as to have inside space enough
to accommodate the circuitry 31 and other components.

[0027] In accordance with an exemplary embodiment, the pressure
transmitter 1 according to the present disclosure also includes an
interface body 20 which is connected to the support body 4 and which is
made of a metallic material (hereinafter referred to as a "second
material"), which is different from the first material of the supporting
body 4.

[0028] In addition, the pressure transmitter 1 includes at least one
isolation diaphragm 21 (hereinafter referred to as a "first isolation
diaphragm") which is positioned onto the interface body 20. In accordance
with an exemplary embodiment, the first isolation diaphragm 21 can be
made of the same material of the interface body 20.

[0029] For example, the first isolation diaphragm 21 can be fixed onto the
interface body 20 so as to have (with respect to the interface body 20
itself) its external surface suitable (e.g., configured) for interfacing
with a process fluid whose pressure is to be measured.

[0030] In accordance with an exemplary embodiment, the second material of
the interface body 20 (and of the first isolation diaphragm 21 according
to an exemplary embodiment) is selected from the group consisting of:
nickel-based alloys, duplex and super-duplex stainless steel materials.
According to an exemplary embodiment, the interface body 20 and the
isolation diaphragm 21 are made of nickel-based alloys commercially known
as MONEL 400 or MONEL K500.

[0031] In accordance with an exemplary embodiment, the first isolation
diaphragm 21 is welded (e.g., laser welded) onto the support interface
body 20.

[0032] The interface body 20 can be differently shaped according to
various applications. For instance, the interface body 20 may be
ring-shaped, disc shaped, or might have a substantial fully solid body
(e.g., a full cylinder body).

[0033] For example, in the exemplary embodiment illustrated in FIG. 1, the
interface body 20 has a substantially full body provided at one end
surface with a corrugated surface 23 on which the first isolation
diaphragm 21 is fixed (e.g., laser welded) and with a cross section
featuring a step 25.

[0034] As illustrated, in the exemplary embodiment of FIG. 1, the
interface body 20 is positioned at one end surface of the support body 4
and is connected to the support body 4 itself.

[0035] In accordance with an exemplary embodiment, the interface body 20
can be welded (e.g., laser welded) onto the support body 4 along at least
a first welding seam 24.

[0036] For example, according to the exemplary embodiment illustrated in
FIG. 1, the interface body 20 is connected to the support body 4 along a
surface 22 transversal with respect to the first isolation diaphragm 21
(and parallel to a reference longitudinal axis 100). In accordance with
an exemplary embodiment, the location of the welding seam 24 on the
transversal surface 22 along which the interface body 20 is connected to
the support body 4 is spaced apart from the first isolation diaphragm 21.

[0037] In this way, the mechanical characteristics of the diaphragm 21 are
not negatively affected by the joining process.

[0038] Further, in the exemplary embodiment illustrated in FIG. 1, on the
support body 4 there is provided another isolation diaphragm 5
(hereinafter referred to as a "second isolation diaphragm").

[0039] The second isolation diaphragm 5 is, for example, welded (e.g.,
laser welded) onto the support body 4 and is in fluid communication with
the pressure sensor 3 by means of a hydraulic circuit 6 filled with a
fluid (e.g., an incompressible fluid, such as a silicon oil).

[0040] The second isolation diaphragm 5 includes, for example, a thin
elastic membrane made of metal such as, for example, AISI 316L, or a
suitable nickel-based alloy.

[0041] As illustrated in FIG. 1, the first isolation diaphragm 21 is also
in fluid communication with the pressure sensor 3 via a hydraulic circuit
60 which is equivalent to the circuit 6 and is filled with the same
and/or a similar type of incompressible fluid. The hydraulic circuit 60
includes a section 61, for example, a through channel 61 provided on the
interface body 20, and a thin gap 62 left between the interface body 20
and the support body 4.

[0042] In accordance with an exemplary embodiment, the first isolation
diaphragm 21 is arranged--for example, its thickness and size and any
other suitable parameters--are selected so as to have along the axis 100
substantially the same linear displacement of that of the second
isolation diaphragm 5 when the first and the second isolation diaphragms
21, 5 are subject to substantially the same level of pressure exerted on
them by the incompressible fluid of the circuit 6 and by the process
fluid, respectively.

[0043] In the exemplary embodiment illustrated in FIGS. 2 and 3, the
interface body 20 has a disc-shaped configuration which is positioned
around the support body 4 so as to embrace a portion thereof, and also
has a corrugated surface 23 on which the first isolation diaphragm 21 is
positioned.

[0044] In accordance with an exemplary embodiment, there are provided two
isolation diaphragms 21 which are fixed (e.g., laser welded) onto the
corrugated surface 23 so that each of them has its external surface
suitable for interfacing with the process fluid whose pressure is to be
measured.

[0045] In this case, both isolation diaphragms 21 can be made of the same
material of the interface body 20, namely, a second material selected
from the group consisting of: nickel-based alloys, duplex or super-duplex
stainless steel materials, for example, a nickel-based alloys
commercially known as MONEL 400 or MONEL K500.

[0046] As illustrated, the two isolation diaphragms 21 are fixed onto the
interface body 20 opposite to each other with respect to the reference
longitudinal axis 100 and extend substantially parallel to the axis 100
itself, while in the exemplary embodiment of FIG. 1, the isolation
diaphragm 21 (and the second isolation diaphragm 5 as well) is positioned
transversal with respect to the longitudinal axis 100.

[0047] The two isolation diaphragms 21 are in fluid communication with the
pressure sensor 3 via a hydraulic circuit (equivalent to that illustrated
in FIG. 1) which is filled with an incompressible fluid, such as a
silicon oil, and includes (for each side) a through channel 61, a thin
gap 62 and passageways 63 provided onto the support body 4.

[0048] In accordance with an exemplary embodiment, the interface body 20
can be welded (e.g., laser welded) onto the support body 4.

[0049] For instance, according to this exemplary embodiment, the interface
body 20 is connected to the support body 4 on a surface 22 substantially
parallel to the couple of first isolation diaphragms 21 along a first
welding seam 24 which is spaced apart from the isolation diaphragms 21
themselves.

[0050] In this way, the mechanical characteristics of the diaphragm 21 are
not negatively affected by the joining process.

[0051] According to an exemplary embodiment illustrated in more detail in
FIG. 3, the interface body 20 (seen in cross-section) includes a first
portion 30 and a second portion 40. The first portion 30 has a thickness
31 smaller than the thickness 41 of the second portion 40. The interface
body 20 is welded (e.g., laser welded) onto the support body 4 along a
second welding seam 26 located at the first portion 30 and spaced apart
from the first welding seam 24 (and the isolation diaphragms themselves).

[0052] In practice, when the pressure transmitter is mechanically
connected to a pipe of the process, for example, by means of one or more
flanges, the first portion 30 forms a thin flexible rim which allows
absorbing possible deformations and therefore reducing consequent error
measurements induced by this mechanical connection.

[0053] The same result may be achieved by suitably sizing the step 25 of
the interface body 20 illustrated in FIG. 1.

[0054] In practice, it has been seen how the pressure transmitter 1
according to the present disclosure achieves the intended object of
providing improvements over known solutions. For example, the purposive
introduction of the interface body 20 and the selection of the same
material for the interface body 20 and the isolation diaphragm(s) 21
realizes a junction between these two elements which does not lead to a
deterioration of the characteristics of the interfacing isolation
diaphragm, thus preventing problems of corrosion inception typical of
known solutions.

[0055] The pressure transmitter 1 thus conceived may undergo numerous
modifications and variants all coming within the scope of the inventive
concept as specified by the appended claims. For example, the interface
body 20 and/or the support body 4 can have a different shape or size, the
hydraulic circuits 6, 60 can be differently shaped, etc., provided that
such possible modifications are compatible with the functions the various
elements are required to perform.

[0056] Moreover, all parts/components can be replaced with other
technically equivalent elements. For example, the type of materials
within the scope of the foreseen applications described above, and the
dimensions, can be any according to needs and to the state of the art.

[0057] Thus, it will be appreciated by those skilled in the art that the
present invention can be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
presently disclosed embodiments are therefore considered in all respects
to be illustrative and not restricted. The scope of the invention is
indicated by the appended claims rather than the foregoing description
and all changes that come within the meaning and range and equivalence
thereof are intended to be embraced therein.